(a) Technical Field
The present invention relates to a master batch elastomer containing organically modified silica and a method for preparing the same. More particularly, the present invention relates to a master batch elastomer containing organically modified nanosilica having an aliphatic hydrophobic group and thus having maximized dispersibility as a tire reinforcing material and a dispersibility method for preparing the same.
(b) Background Art
In general, a tire tread is prepared by blending rubber with a filler. Typically, the rubber is a blend of a styrene-butadiene copolymer and a conjugated diene rubber, and the filler is carbon black, silica or a mixture thereof, as a reinforcing material.
Silica, being an eco-friendly material, has been gaining attentions as a tire filler material in the situation where environmental regulations become stricter and oil prices remain high. As a filler material for the so-called “green tire”, its use is increasing rapidly. However, use of silica as the reinforcing material is problematic in that the silica particles tend to agglomerate through interaction to form large clusters, resulting in poor dispersibility. Since the dispersing of silica in rubber greatly affects the wearing and lifespan of a tire, it is desired to maximize the dispersibility of silica.
Often, a master batch type elastomer is prepared by mixing with carbon black in order to improve dispersibility of the reinforcing material and to simplify the tire manufacturing process. However, preparation of a silica master batch elastomer using a diene-based copolymer prepared by solution polymerization in commercial scale is limited since most of silica is lost during the steam stripping process because of the hydrophilicity of silica.
On the other hand, when hydrophobic silica is used as the tire reinforcing material, it is difficult to attain mechanical properties required for the tire because chemical bonding with rubber is impossible.
Various methods for more effective use of silica have been proposed to maximize its dispersibility and ensure good mechanical properties.
U.S. Pat. No. 5,925,713 proposes a technique of modifying the end group using a monomer having an epoxy group in order to improve affinity to a filler, and Korean Patent Application Publication Nos. 1994-019797 and 1994-019795 disclose examples of improving abrasion resistance and impact resistance by dispersing polydimethylsiloxane in the composition.
In addition, there have been various researches to modify the end group of rubber in order to improve dispersibility of silica used as a reinforcing filler of a tire. However, there has been limitation in improving the dispersibility of the filler only with the introduction of functional end groups. Some silica manufacturers have introduced a technique of preparing a silica master batch elastomer consisting of rubber and general-use silica using a specialized facility. However, due to the agglomeration of silica, the silica tends not to be sufficiently dispersed in the rubber and Mooney viscosity of the compound tends to increase, resulting in problems during processing and manufacturing of the tire [DKT 2006 Poster 33 “Rubber Filler Composition Based on Solution Polymers and Silica—Status of Developments”].
International Patent Application Publication No. WO 1998/37015 (Korean Patent Application Publication No. 2000-0075614) proposes hydrophobic silica having improved compatibility with rubber. But, although the use of hydrophobic silica as a tire reinforcing material improves compatibility with rubber, modulus, tensile property and abrasion property of the tire degrade greatly due to the difficulty in forming chemical bonding with the rubber.
Further, although Korean Patent Application Publication No. 2002-0021407 proposes a method of mixing latex rubber prepared by emulsion polymerization with silica or carbon black to prepare a silica or carbon black master batch for a tire. However, the copolymer prepared by emulsion polymerization tends not to exhibit the rolling resistance, high wet traction and low heat generation required for a high-performance tire.
As described above, a silica master batch elastomer having satisfactory properties has not been developed as yet.